Quartz Glass
When silicon dioxide SiO2 is cooled rapidly enough, it does not crystallize but solidifies as a glass. The glass transition temperature of pure SiO2 is about 1600 K (1330 °C or 2420 °F). Like most of the crystalline polymorphs the local atomic structure in pure silica glass is regular tetrahedra of oxygen atoms around silicon atoms. The difference between the glass and the crystals arises in the connectivity of these tetrahedral units. SiO2 glass consists of a non-repeating network of tetrahedra, where all the oxygen corners connect two neighbouring tetrahedra. Although there is no long range periodicity in the glassy network there remains significant ordering at length scales well beyond the SiO bond length. One example of this ordering is found in the preference of the network to form rings of 6-tetrahedra.
Read more about this topic: Silicon Dioxide
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